Image processing apparatus and image processing method

ABSTRACT

A characteristic image detection interpolation unit performs interpolation processing for increasing the luminance value in low-luminance area which is partly present in an input image. A minimum value filter unit executes minimum value filter processing on an image subjected to the interpolation processing, and a low-pass filter performs low-pass filter processing on the image subjected to the minimum value filter processing, thereby generating a low-frequency component image. A subtracter generates a high-frequency component image by subtracting the low-frequency component image from the input image. A coefficient multiplier adds the luminance value of the high-frequency component image to the input image by a preset ratio K 1 , thereby generating a high-frequency component enhanced image. A selector alternately outputs the low-frequency component image and the high-frequency component enhanced image.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing technique.

2. Description of the Related Art

In recent years, a liquid-crystal display device has been used as atelevision receiver or a display device for a PC. Such a liquid-crystaldisplay device has been widely used because it can be formed thin andsaves space and power. In such a liquid-crystal display device, however,the response time for motion video is long.

As a driving method for a liquid-crystal display device to improve theresponse time, there has been provided a method of comparing image datato be displayed next with previous image data, and performing overdrivein accordance with the comparison result (Japanese Patent Laid-Open No.11-126050).

As a method of improving motion blurring due to the displaycharacteristics of a liquid-crystal display device, there has beenproposed a method of driving the display device by doubling the framefrequency of an input image signal, and by inserting a black image or anintermediate image (Japanese Patent Laid-Open No. 2002-351382).

Furthermore, the following technique has been proposed (Japanese PatentLaid-Open No. 2006-184896). One frame is divided into a plurality ofsubframes by raising the frame frequency of an input image signal.High-frequency components of an image signal used to display an image inat least one predetermined subframe of the plurality of subframes aredecreased as compared with image signals used to display images in othersubframes.

If the change amount of the high-frequency components is large, however,a value exceeding a display range may be generated, thereby disturbingthe display image or displaying an extra video. If this problem isaddressed by decreasing the high-frequency components, the motionblurring improvement effect decreases (deteriorates).

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aboveproblems, and provides a technique for allowing a display taking fulladvantage of the dynamic range of display tones without losinghigh-frequency components, and for suppressing extra pseudo components.

According to a first aspect of the present invention, an imageprocessing apparatus comprises:

a correction unit which increases a luminance value in a low-luminancearea that is partly present in an input image;

a filter unit which generates a low-frequency component image byexecuting minimum value filter processing on an image corrected by thecorrection unit and then performing low-pass filter processing on theimage subjected to the minimum value filter processing;

a unit which generates a high-frequency component image by subtractingthe low-frequency component image from the input image;

an unit which generates a high-frequency component enhanced image byadding a luminance value of the high-frequency component image to theinput image according to a preset ratio; and

an output unit which alternately outputs the low-frequency componentimage and the high-frequency component enhanced image.

According to a second aspect of the present invention, an imageprocessing method comprises:

a correction step of increasing a luminance value in a low-luminancearea which is partly present in an input image;

a filter step of generating a low-frequency component image by executingminimum value filter processing on an image corrected in the correctionstep and then performing low-pass filter processing on the imagesubjected to the minimum value filter processing;

a step of generating a high-frequency component image by subtracting thelow-frequency component image from the input image;

a step of generating a high-frequency component enhanced image by addinga luminance value of the high-frequency component image to the inputimage according to a preset ratio; and

an output step of alternately outputting the low-frequency componentimage and the high-frequency component enhanced image.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of the functionalarrangement of an image processing apparatus 200 according to the firstembodiment;

FIG. 2 is a block diagram showing an example of the functionalarrangement of a subframe image generation unit 103;

FIGS. 3A to 3E are charts showing examples of the waveform of a videosignal;

FIG. 4 is a block diagram showing an example of the functionalarrangement of a subframe image generation unit 103;

FIGS. 5A to 5C are charts showing examples of the waveform of a videosignal; and

FIG. 6 is a flowchart showing processing executed by the imageprocessing apparatus 200.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described below withreference to the accompanying drawings. Note that the embodiments to beexplained below are merely examples when the present invention ispractically implemented, and are practical examples of an arrangementset forth in the following claims.

First Embodiment

With reference to FIG. 1, an image processing apparatus and itsperipherals according to this embodiment will be described first. Asshown in FIG. 1, an image processing apparatus 200 according to theembodiment connects with a PC (Personal Computer) 300, and can acquire avideo signal as a display target from this PC 300. The image processingapparatus 200 has an AV terminal 51, and can externally receive, via theAV terminal 51, signals of various standards such as NTSC, and videosignals of general TV broadcast programs. The image processing apparatus200 can also receive, via the AV terminal 51, a video signal from, e.g.,a recording device (video deck, DVD recorder, or HDD recorder) forrecording a video signal on a medium, or a playback device (DVD player,LD player, or the like) for playing back a video signal recorded on amedium. As explained above, the image processing apparatus 200 canacquire a video signal in various input forms.

The image processing apparatus 200 will be described first. Signals ofvarious standards, such as NTSC, video signals of general TV broadcastprograms, and video signals output from a recording device such as avideo deck, DVD recorder, or HDD recorder, or a playback device such asa DVD player or LD player are input to a signal processing circuit 52via the AV terminal 51.

The signal processing circuit 52 performs signal processing such asdecoding, noise reduction, bandwidth-limiting filtering, and signallevel adjustment on the video signal input via the AV terminal 51. Thesignal processing circuit 52 sends the video signal subjected to thevarious signal processes to a subsequent switch 30.

In addition, a video signal transmitted from the PC 300 is input to theswitch 30 via a terminal 50. The switch 30 then selects one of the videosignals from the signal processing circuit 52 and the terminal 50, andsends the selected video signal to an A/D converter 31. The A/Dconverter 31 converts the video signal serving as an analog video signalsent from the switch 30 into a digital video signal.

A DSP (Digital Signal Processor) 32 performs image processing such ascontrast adjustment, brightness control, color conversion, andresolution conversion on the digital video signal input from the A/Dconverter 31. The DSP 32 sends a resultant video signal to a subsequentframe rate conversion unit 101.

The frame rate conversion unit 101 converts the frame rate of the videosignal input from the DSP 32. The frame rate conversion unit 101 storesthe converted video signal as image data in a memory 33. The memory 33is used for storing the image data of a current frame (image data to bedisplayed now) and that of the next frame (image data to be displayed inthe next frame). Therefore, the frame rate conversion unit 101sequentially sends the image data stored in the memory 33 to asubsequent subframe image generation unit 103 from the older data.

A timing generation circuit (TG) 34 outputs a timing signal whichdefines an operation timing of each unit of a signal processing unit 3to the corresponding unit. The subframe image generation unit 103performs, on the image data sent from the frame rate conversion unit101, processing for improving a moving image characteristic such asmotion blurring, thereby generating and outputting a low-frequencycomponent image and a high-frequency component enhanced image (to bedescribed later).

A timing detection unit 132 supplies, to the subframe image generationunit 103, a switching signal for causing the subframe image generationunit 103 to alternately output the low-frequency component image and thehigh-frequency component enhanced image. A polarity inversion unit 106inverts the polarity of a video signal based on the image data outputfrom the subframe image generation unit 103.

A D/A converter 35 converts the video signal serving as a digital videosignal whose polarity has been inverted by the polarity inversion unit106 into an analog video signal, and sends it to a subsequent paneldriver 36.

Of the video signal received from the D/A converter 35, the panel driver36 sends an R component signal to an R panel 2R, a G component signal toa G panel 2G, and a B component signal to a B panel 2B. The panel driver36 also supplies power to the panels 2R, 2G, and 2B. The above-describedunits constitute the signal processing unit 3.

Each panel 2R, 2G, or 2B functions as a display device, which displaysthe image of a corresponding color component. Note that although asignal input to the image processing apparatus 200 is an analog videosignal in FIG. 1, a digital video signal input terminal for, e.g., LVDSor TMDS, or a D4 terminal for digital TV may be provided to input adigital video signal.

A ballast 57 is a lamp power supply connected to a lamp 1. The imageprocessing apparatus 200 includes a power supply 58 and an AC inlet 60.A remote controller 61 is operated by a user to give variousinstructions to the image processing apparatus 200. A control panel 62receives signals from the remote controller 61, and notifies a CPU 63 ofthem.

The CPU 63 uses computer programs and data stored in a ROM 64 to controlthe operation of the units of the image processing apparatus 200. TheROM 64 stores computer programs and data for causing the CPU 63 tocontrol the operation of the units of the image processing apparatus 200so that the units execute processes to be described later. A RAM 65includes an area for temporarily storing various externally receiveddata, and a work area which is used by the CPU 63 to execute variousprocesses. That is, the RAM 65 can provide various areas as needed. AUSB interface (I/F) 107 is used to communicate data with the PC 300 viaa terminal 121.

Assume that the above units of the image processing apparatus 200 areconnected with each other via a common bus so that they can execute datacommunication. The arrangement of the image processing apparatus 200need not strictly conform to FIG. 1, as a matter of course. Anyarrangement may be adopted as long as it is possible to implement theprocesses to be described below. This embodiment is explained on theassumption that the all units of the image processing apparatus 200shown in FIG. 1 are configured by hardware components. It is, however,also possible to achieve the functions of the units by implementing thesubframe image generation unit 103, the frame rate conversion unit 101,and the like as computer programs, storing them in the ROM 64, and thenexecuting them by the CPU 63.

The operation of the frame rate conversion unit 101 will now bedescribed in more detail. The frame rate conversion unit 101 divides oneframe video signal into N subframe video signals. N is an arbitraryinteger larger than 1. The frame rate rises by N times in accordancewith the division number. In this embodiment, an example of N divisionwill be explained in which N=2, and more specifically, a video signalhaving a vertical frequency of 60 Hz is converted into a signal having avertical frequency of 120 Hz obtained by doubling the vertical frequencyof 60 Hz. At this time, input image data of at least one frame is storedin the memory 33. By changing the speed of reading out image data fromthe memory 33, the input video signal can be transformed into a videosignal having a different frame rate.

With reference to FIG. 2, an example of the functional arrangement ofthe subframe image generation unit 103 and its operation will beexplained next.

The image data sent from the frame rate conversion unit 101 is input toan input terminal 202, and then input to a gamma conversion unit 203 viathe input terminal 202. The gamma conversion unit 203 performs gammaconversion with a power of 2.2 on the image data input via the inputterminal 202 to convert it into image data with a linear gammacharacteristic.

A characteristic image detection interpolation unit 204 executesprocessing of increasing the luminance value in a low-luminance area byinterpolating the low-luminance area, by using its surrounding area,which is partly present in an image (input image) indicated by the imagedata converted by the gamma conversion unit 203. For example, in orderto remove a characteristic image such as an isolated point or fine linefrom the input image, the unit 204 interpolates the area of thecharacteristic image by using its surrounding area.

A minimum value filter unit 205 performs minimum value filter processingon an image indicated by the image data which has been subjected tointerpolation processing by the characteristic image detectioninterpolation unit 204. As is well known, the minimum value filterprocessing detects a minimum pixel value (luminance value) in a pixelarea including a pixel of interest and a group of neighboring pixels.The processing then updates the pixel value of the pixel of interestwith the detected pixel value. Performing this processing by settingeach pixel of the image as a pixel of interest enables the minimum valuefilter unit 205 to execute the minimum value filter processing on thewhole image.

A low-pass filter (LPF) 206 performs low-pass filter processing using alow-pass filter such as a Gaussian filter on the image data which hasbeen subjected to the minimum value filter processing by the minimumvalue filter unit 205. This makes is possible to generate alow-frequency component image (L) in which high-frequency componentshave been cut. The low-pass filter 206 sends the generated low-frequencycomponent image to a subsequent selector 210 and a subtracter 207.

The subtracter 207 subtracts the low-frequency component image (L)generated by the low-pass filter 206 from the input image (H+L)converted by the gamma conversion unit 203, thereby generating ahigh-frequency component image (H).

A coefficient multiplier 208 adjusts the luminance value of each pixelof the high-frequency component image by multiplying the high-frequencycomponent image (H) generated by the subtracter 207 by a predeterminedcoefficient K1, and sends the adjusted high-frequency component image toan adder 209.

The adder 209 composites the input image (H+L) converted by the gammaconversion unit 203 and the high-frequency component image whoseluminance values have been adjusted by the coefficient multiplier 208,thereby generating a high-frequency component enhanced image (2H+L).That is, the high-frequency component enhanced image can be obtained byadding the luminance values of the high-frequency component image to theinput image (H+L) by a preset ratio (K1).

The selector 210 alternately selects the high-frequency componentenhanced image (2H+L) generated by the adder 209 and the low-frequencycomponent image (L) generated by the low-pass filter 206 in accordancewith a switching signal input from the timing detection unit 132 via aterminal 201. The switching period is 120 Hz. The selector 210 thensends the selected image to a subsequent gamma conversion unit 211. Thegamma conversion unit 211 performs gamma conversion on the image outputfrom the selector 210 as needed, and sends a resultant video signal tothe polarity inversion unit 106 via a terminal 212.

A video signal (image data) which varies during processing executed bythe subframe image generation unit 103 will be described next usingFIGS. 3A to 3E. Charts shown in FIGS. 3A to 3E respectively show thewaveforms of video signals for one line in the horizontal direction.Assume that the background is black (a luminance signal level=0) and theforeground is white (a luminance signal level=100).

A video signal having the waveform shown in FIG. 3A does not include acharacteristic image such as an isolated point or fine line. When thevideo signal is input, therefore, the characteristic image detectioninterpolation unit 204 outputs a video signal having the same waveformas that shown in FIG. 3A, as shown in FIG. 3B.

When the video signal having the waveform shown in FIG. 3B is input, theminimum value filter unit 205 outputs a video signal having the waveformshown in FIG. 3C. As described above, the minimum value filterprocessing executed by the minimum value filter unit 205 detects aminimum luminance value from a pixel of interest and a group ofneighboring pixels (N pixels around the pixel of interest), and replacesthe luminance value of the pixel of interest with the detected luminancevalue. Consequently, an area having a low luminance level spreads.

A case in which a video signal including a characteristic image such asan isolated point or fine line is input to the characteristic imagedetection interpolation unit 204 will be explained next. The videosignal including a characteristic image such as an isolated point orfine line has a waveform in which an area having a low luminance levelis partly present in an area having a high luminance level, as shown inFIG. 3D. Assume that the characteristic image detection interpolationunit 204 is omitted from the image processing apparatus 200, and thevideo signal having the waveform shown in FIG. 3D is input to theminimum value filter unit 205. In this case, as shown in FIG. 3E, avideo signal having a waveform in which the area having the lowluminance level spreads is output.

In this embodiment, even if the video signal having the waveform shownin FIG. 3D is input, it is possible to solve the above problems sincethe characteristic image detection interpolation unit 204 detects aluminance difference between a pixel of interest and its neighboringpixels, and corrects and removes the area having a low luminance level.That is, it is possible to prevent a minute black area shown in FIG. 3Dfrom spreading due to the minimum value filter processing.

This embodiment has an advantage that a characteristic point remains inthe high-frequency component enhanced image without correction. This,therefore, makes it possible to improve only a defect in acharacteristic point for a minimum value filter without degradation suchas a loss of a characteristic image in an image finally displayed.

The above-mentioned processes executed by the image processing apparatus200 will be explained with reference to FIG. 6 which shows a flowchartof the processes. Note that the processes are as described above, andwill be briefly explained here.

In step S601, as described above, for a video signal input via theswitch 30, the A/D converter 31 and the DSP 32 perform video signalconversion into a digital video signal and various image processes onthe digital video signal, respectively.

In step S602, the frame rate conversion unit 101 converts the frame rateof the video signal input from the DSP 32. In step S603, the gammaconversion unit 203 performs gamma conversion on image data input viathe input terminal 202 to convert it into image data with a linear gammacharacteristic.

In step S604, the characteristic image detection interpolation unit 204executes processing of increasing a luminance value in a low-luminancearea by performing the above interpolation processing on an imageindicated by the image data converted by the gamma conversion unit 203.

In step S605, the minimum value filter unit 205 performs the minimumvalue filter processing on the image indicated by the image data whichhas been subjected to the interpolation processing by the characteristicimage detection interpolation unit 204. In step S606, the low-passfilter (LPF) 206 executes the low-pass filter processing on the imagedata which has been subjected to the minimum value filter processing bythe minimum value filter unit 205, thereby generating a low-frequencycomponent image in which high-frequency components have been cut.

In step S607, the subtracter 207 generates a high-frequency componentimage by subtracting the low-frequency component image from the imageconverted by the gamma conversion unit 203. In step S608, thecoefficient multiplier 208 adjusts the luminance value of each pixel ofthe high-frequency component image generated by the subtracter 207 bymultiplying the high-frequency component image by the predeterminedcoefficient K1.

In step S609, the adder 209 composites the image converted by the gammaconversion unit 203 and the high-frequency component image whoseluminance values have been adjusted by the coefficient multiplier 208,thereby generating a high-frequency component enhanced image.

In step S610, the selector 210 alternately selects, in accordance with aswitching signal, the high-frequency component enhanced image generatedby the adder 209 and the low-frequency component image generated by thelow-pass filter 206, and sends the selected image to the gammaconversion unit 211. The gamma conversion unit 211 performs gammaconversion on the image output from the selector 210 as needed, andsends a resultant video signal to the polarity inversion unit 106 viathe terminal 212.

In step S611, of the video signal subjected to the processing by thepolarity inversion unit 106, the D/A converter 35, and the panel driver36, an R component video signal, a G component video signal, and a Bcomponent video signal are respectively sent to the panels 2R, 2G, and2B.

Second Embodiment

In the first embodiment, the characteristic image detectioninterpolation unit 204 interpolates a low-luminance area, by using itssurrounding area, which is partly present in an image indicated by avideo signal converted by the gamma conversion unit 203, therebyincreasing the luminance value in the low-luminance area. In the secondembodiment, as another method for increasing the luminance value in alow-luminance area, a low-pass filter is used. That is, in the secondembodiment, a low-pass filter is used instead of the characteristicimage detection interpolation unit 204.

In this embodiment, therefore, the arrangement of a subframe imagegeneration unit 103 is the same as in the first embodiment except that alow-pass filter 1001 is substituted for the characteristic imagedetection interpolation unit 204, as shown in FIG. 4. The low-passfilter 1001 performs low-pass filter processing on a video signalconverted by a gamma conversion unit 203, thereby increasing theluminance value in a low-luminance area.

If a video signal having a waveform, in which an area having alow-luminance level is partly present in an area having a high-luminancelevel as shown in FIG. 5A, is input to the low-pass filter 1001, thelow-pass filter 1001 increases the luminance value in the low-luminancearea as shown in FIG. 5B. If a video signal having a waveform shown inFIG. 5B is input to a minimum value filter unit 205, the minimum valuefilter unit 205 prevents a minute black area from spreading due tominimum value filter processing, as shown in FIG. 5C.

According to the above embodiments, even when a moving imagecharacteristic such as moving image blurring is improved, display takingfull advantage of the dynamic range of display tones is possible withoutlosing high-frequency components. This makes it possible to improve amoving image characteristic without deterioration of the image qualityby a characteristic image such as an isolated point.

Other Embodiments

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiment(s), and by a method, the steps ofwhich are performed by a computer of a system or apparatus by, forexample, reading out and executing a program recorded on a memory deviceto perform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-232864 filed Oct. 6, 2009, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image processing apparatus comprising: acorrection unit which increases a luminance value in a low-luminancearea that is partly present in an input image, by interpolating thelow-luminance area using its surrounding area; a filter unit whichgenerates a low-frequency component image by executing minimum valuefilter processing on an image corrected by said correction unit and thenperforming low-pass filter processing on the image subjected to theminimum value filter processing; an unit which generates ahigh-frequency component image by subtracting the low-frequencycomponent image from the input image; an unit which generates ahigh-frequency component enhanced image by adding a luminance value ofthe high-frequency component image to the input image according to apreset ratio; and an output unit which alternately outputs thelow-frequency component image and the high-frequency component enhancedimage.
 2. The apparatus according to claim 1, wherein the input image isan image which is represented by a video signal with a linear gammacharacteristic and is obtained by performing gamma conversion on anexternally input image.
 3. The apparatus according to claim 1, whereinsaid output unit performs gamma conversion on the image to be output,and then outputs the image subjected to the gamma conversion.
 4. Theapparatus according to claim 1, wherein said output unit outputs animage to a display device.
 5. An image processing method comprising: acorrection step of increasing a luminance value in a low-luminance areawhich is partly present in an input image, by interpolating thelow-luminance area using its surrounding area; a filter step ofgenerating a low-frequency component image by executing minimum valuefilter processing on an image corrected in the correction step and thenperforming low-pass filter processing on the image subjected to theminimum value filter processing; a step of generating a high-frequencycomponent image by subtracting the low-frequency component image fromthe input image; a step of generating a high-frequency componentenhanced image by adding a luminance value of the high-frequencycomponent image to the input image according to a preset ratio; and anoutput step of alternately outputting the low-frequency component imageand the high-frequency component enhanced image.